The Specific Aims of this Core are: 1) To make readily available flow and image cytometry and cell sorting instrumentation and techniques to Program Project research. 2) To assist investigators in finding appropriate ways to apply cytometric techniques to their research objectives. The Core operates 4 cytometers, providing instrumentation that best matches the needed application. These are: an ELITE cell sorter; an ORTHO 50/2150 cell sorter, an ICP-22 non-sorting cytometer and an ACAS (Adherent Cell Analysis and Sorting) 570 imaging and confocal cytometer, In addition, software in support of Core cytometry services is developed and applied. The Core will provide the Program Project both scientific expertise and access to advanced instrumentation and software. Cytometry and cell sorting will be essential parts of each of the Projects, providing both preparative (cell purification by sorting) and analytical services. Types of Cytometric analyses and sorting that will be performed include: 1) Sorting lymphocyte subsets; 2) Assays of cell proliferation and Cell Cycle; 3) Analysis of Heterokaryon and Cytoplast cell fusion products; 4) Alkaline unwinding DNA damage and repair assays. 5) Measurement of mitochondrial membrane potential and cellular redox status; 6) Measurement of Apoptosis; 7) Quantitating Intracellular Calcium and Glutathione or pH; 8) Sorting of transfected cells and characterization of transgenic mouse tissues.